Build status

News

2014-07-01

2014-04-17

You can now insert PyStache {{}} style variables to import
environment variables.

stack:
ami_id: {{AMIID}}
AMID=ami-1q23123123 cumulus -y example_stack.yaml -a create
would be seen by cloudformation with the ami id of ami-1q23123123

2013-09-06

You can now define stack level tags using the tags directive in the
YaML file, like:

tags:
tag1: value
tag2: value

tags can be specified both
at root level and sub-stack level. tags at root level are applied to all
sub-stacks and duplicate sub-stack tags will override root level tags

You can use the directive disable: true in any sub-stack to prevent it from being created/updated/deleted

The problem

Amazon CloudFormation (CF) allows you to instantiate multiple AWS
resources in a repeatable, ordered and structured method. As our
infrastructure grew, so did our CF templates and soon they were
monolothic and complex to maintain. We looked at spliting these
templates into smaller chunks, which worked as a short term solution but
created a new problem. With multiple templates dependant on other
declared resources, we were forced to manually pass parameters for
inter-stack operability. This greatly affected the repeatability of our
stacks as we did not have an easy method to keep track of what
parameters were used, especially those relating to physical resource
IDs.

The solution

Cumulus attempts to solve the problem by introducing a layer above CF
templates, a stack configuration YAML file. This allows multiple CF
stacks to be created in order and maintained respecting their
dependencies. The YAML file stores values for parameters to be passed
into each of the stacks. Parameters can be assigned with static values
or will source the value of a parameter, output or resource of another
stack described in the YAML file. Cumulus actively translates reference
values to physical resource values on creation of the stack.

Current state / known issues

For our use, Cumulus can create, update and delete stacks reliably but
is still very much in an Alpha state. We’re looking forward to see how
you use Cumulus, and please submit pull requests for any issues you may
encounter or for feature requests :)

This is my first real python project, so I’m sure the code can be, just
generally better…

Known issues:

Templates are passed in as a JSON string to CF, this will break large
templates

Roadmap:

Implement a way of displaying meaningful diffs during update runs

Add support for using S3/Externally hosted templates

Support larger templates

How to get started

Clone the repo somewhere:

$ git clone git://github.com/cotdsa/cumulus.git

Install Cumulus with setuptools:

$ sudo python setup.py install

Make sure you have AWS credentials set up for boto (the library used by
Cumulus to interact with AWS). Set the following environment variables:

AWS_ACCESS_KEY_ID - Your AWS Access Key ID

AWS_SECRET_ACCESS_KEY - Your AWS Secret Access Key

or create a boto config file as described
here, covering some
other helpful boto-related settings.

Creating the example stack

Common sense warning: Running this example will create real
resources in AWS and will cost you AWS credits / money / magic beans.

I have included an example stack in the examples/ dir. It consists of
three files:

cumulus_example_stack.yaml: The Cumulus yaml file for the stack.
Creates a stack out of the following two templates in ap-southeast-2
(Sydney region)

vpc_layer.json: CF template to creates a VPC, base subnet and ACL

instance_layer.json: CF template to create an instance inside a
given VPC

The template files are complete and work independently of Cumulus.
Cumulus’s purpose in life is just to make managing them easier.

To create the example stack, change into the examples/ dir and run:

$ cumulus -y cumulus_example_stack.yaml -a create

Cumulus will print out CF messages as it builds.

You can then try modifying the template and/or the values of the
parameters and then update the stack: